1. Field of the Invention
The present invention relates to a method for controlling Asian soybean rust (ASR) of a conventionally bred ASR-tolerant, Stem canker resistant and/or Frog-eye leaf spot resistant soybean variety comprising the application of a succinate dehydrogenase inhibitor (SDHI) fungicide to said plant, plant propagation material, or at its locus of growth.
2. Description of Related Art
Soybean (genus Glycine) is considered to be an important crop and is highly valued by world agriculture. Therefore, one of the major objectives of the soybean breeders is to develop more stable, productive and disease-resistant varieties. The basic motivation is to maximize grain yield for human and animal consumption. In order to attain said objects, the breeder usually selects varieties having superior traits.
Asian soybean rust (ASR), caused by the fungus Phakopsora pachyrhizi, is considered to be the most destructive soybean leaf disease (Miles, M. R.; Frederick R. D.; Hartman, G. (2003) Soybean rust: Is the U. S. soybean crop at risk? Online. APSnet Feature, American Phytopathological Society). The disease spreads by windblown uredospores which consequently let to long-distance dispersal to new, rust-free regions. Therefore, ASR has already caused losses in many soybean-growing regions of the world. The impact of the pathogen on productivity is drastic: up to 80% yield loss was observed in some regions (Yorinori J. T. (2004) Ferrugem “asiática” da soja no Brasil: evoluçõ, importáncia econômica e controle. In: Junior J. N. Lazzarotto J. J. (eds.) Documentos 247. Embrapa, Londrina, Brazil, 36).
In order to control the disease, fungicides are applied or resistant or tolerant varieties are used.
The application of fungicides commonly bears the problem of unfavorable environmental or toxicological effects due to high dosage rates which are needed to effectively control the disease.
Fungus resistance is known to naturally occur in genotypes of the Glycine genus (Burdon, J. J.; Marshall, D. R. (1981) Evaluation of Australian native species of Glycine canescens, a wild relative of soybean. Theoretical Applied Genetics, 65: 44-45; Burdon, J. J. (1988) Major gene resistance to Phakopsora pachyrhizi in Glycine canescens, a wild relative of soybean. Theoretical Applied Genetics, 75: 923-928). Five qualitative dominant resistance genes have been identified (Meyer J. D. F., et al., (2009) Identification and analyses of candidate genes for rpp4-mediated resistance to ASR in soybean, Plant Physiology, 150: 295-307; Oloka H. K.; Tukamuhabwa P. (2008) Reaction of exotic soybean germplasm to Phakopsora pachyrhizi in Uganda, Plant Disease, 92: 1493-1496): rpp 1 in PI200492 (McLean, R. J.; Byth, D. E. (1980) Inheritance of resistance to rust (Phakopsora pachyrhizi) in soybean. Australian Journal Agricultural research, 31: 951-956); rpp2 in PI230970 (Bromfield, K. R.; Hartwig E. E. (1980) Resistance to soybean rust and mode of inheritance. Crop Science, 20: 254-255); rpp3 in PI 462312 (Bromfield K. R.; Melching, J. S. (1982) Sources of specific resistance to soybean rust. Phytopathology, 72: 706); rpp4 in PI 459025 (Hartwig R. R. (1986) Identification of a fourth major gene conferring to resistance to soybean rust. Crop Science, 26: 1135-1136) and rpp5 (Meyer J. D. F. (2009) Identification and analyses of candidate genes for Rpp4-mediated resistance to Asian Soybean Rust in soybean. Plant Physiol 150: 295-307). The resistance presented by each gene is limited to the specific pathogen variety and can be overcome in a short period of time due to the coevolution of host resistance and pathogen virulence. Even though there are soybean varieties that have superior traits, e. g. ASR tolerance, they are not fully resistant but still only tolerant to said disease.
Therefore, crop tolerance and activity against fungi do not always satisfy the needs of agricultural practice in many incidents and aspects. The use of new resistance sources are investigated with the focus lying on both: more effective fungicide application and identification and/or modification of genes which confer ASR tolerance/resistance.
WO 2010/049405 teaches a method for improving the health of a plant by the application of a combination containing a heteroaryl-substituted alanine compound and an agriculturally active compound such as for example the fungicides fluxapyroxad, bixafen, boscalid, isopyrazam or penthiopyrad. Therein, the improvement of the plant's health does not indicate a teaching for the control of ASR.
Furthermore, it has been previously reported by US 2010/0093715 that the application of a carboxamide fungicide to a transgenic plant resulted in a synergistic increase of plant health. Although it mentions a method for controlling ASR, the teaching is limited to plants with transgenic modifications. ASR tolerant transgenic plants are not described.
WO 2010/046380 describes a method of controlling pests and/or increasing the health of a plant by treating a cultivated plant with a carboxamide compound. Soybean varieties which are referred to in the description or the examples of this reference are transgenic plants. The soybean variety employed in the biological example of WO 2010/046380 contains a transgene conferring an herbicide tolerance. There is no hint in WO 2010/046380 that the application of a succinate dehydrogenase inhibitor (SDHI) fungicide to an ASR-tolerant, Stem canker resistant and/or Frog-eye leaf spot resistant conventionally bred soybean variety would result in a synergistic effect between the trait of said plant and the applied fungicide. Therefore, no sufficient teaching concerning the control over ASR on conventionally bred or transgenic ASR-tolerant, Stem canker resistant and/or Frog-eye leaf spot resistant soybean varieties is given.
General advantages of conventionally bred vs. transgenic plants include the following:
In many cases, traits introduced by conventional breading are more stable than traits introduced by transgenic methods. For conventionally bred plants, there is less risk of environmental contamination e.g. by horizontal gene transfer. In particular, for conventionally bred plants there is no risk that might be conferred by an antibiotic resistance gene that is routinely introduced in transgenic plants for selection purposes. Also, there is a strong economic advantage generated, as there is no need for expensive and longish deregulation proceedings in each country for conventionally bred plants. Also the timespan and costs needed to develop a conventionally bred variety are much shorter than for transgenic varieties. In addition, in some countries the acceptance by the consumer is generally higher. Further, for conventionally bred plants there is no risk that beneficial plant properties are disturbed or even eliminated by the randomly occurring introduction of the transgene into the genome.